1. Field of the Invention
The present invention relates to a radiant noise inhibiting assembly, and more particularly, to a radiant noise inhibiting assembly constructed to inhibit a radiant noise in an electric cable which is connected to a digital type electronic device.
2. Description of the Related Art
With a digital type electronic device such as a personal computer or a word processor which is controlled by high frequency digital signals, there has long been a problem that a radiant noise will disturb a picture plane of a display monitor connected thereto. To prevent such a problem and to inhibit such radiant noise, it is often necessary to take some countermeasures in an electric cable serving as a data line and an electric cable serving as a power supply line, both connected to a digital type electronic device.
As a practically useful method for inhibiting a radiant noise in an electric cable, it has been suggested that the electric cable be inserted into and through an elongated tubular magnetic member, or alternatively, an electric cable be passed through several ring-shaped core type magnetic members. With the use of the above methods, a common mode noise will be induced in an electric cable. The magnetic member causes an inductance in the electric cable. The inductance and a frequency component of the common mode noise generate an impedance. The impedance can inhibit the above described radiant noise.
FIG. 12 is a perspective view schematically illustrating an arrangement for inhibiting a radiant noise in an electric cable, which has been disclosed in Japanese Unexamined Patent Publication No. 3-211906. As shown in FIG. 12, an electric cable 70 is inserted into and through an elongated tubular, electrically conductive member 71. Then, the electric cable 70 together with the elongated tubular electrically conductive member 71 are further inserted into and through an elongated tubular magnetic member 72. One end of the elongated tubular electrically conductive member 71 is connected to a ground of the electronic device so as to be grounded. In this way, a structure capable of inhibiting a radiant noise in the electric cable 70 may thus be formed. Therefore, by using such an arrangement shown in FIG. 12, it is possible to make use of a function of a magnetic shield provided by the elongated tubular magnetic member 72, and a function of an electrostatic shield provided by the elongated tubular electrically conductive member 71, thereby effectively inhibiting a radiant noise in the electric cable 70.
However, since a digital type electronic device is required to operate and be controlled at a higher and higher speed, the above-discussed arrangement shown in FIG. 12 has been found to be insufficient for inhibiting a radiant noise of an electric cable. Accordingly, it has recently been demanded that a more efficient structure be provided which can be used to more effectively inhibit a radiant noise of an electric cable.
To overcome the problems described above, preferred embodiments of the present invention provide an improved radiant noise inhibiting assembly which is constructed to sufficiently inhibit a radiant noise in an electric cable which is connected to a digital type electronic device.
A radiant noise inhibiting assembly according to a preferred embodiment of the present invention includes a magnetic structure arranged in a longitudinal direction of an electric cable connected to a digital type electronic device, the magnetic structure being arranged to continuously or intermittently cover an entire circumference of the electric cable along a certain range, an electrically conductive structure continuously covering the entire range where the magnetic structure covers the electric cable. In particular, only a first end of the electrically conductive structure is connected to a ground of the electronic device, the first end being closer to the electronic device than a second end of the electrically conductive structure.
In the radiant noise inhibiting assembly of preferred embodiments of the preset invention, an electric cable is covered by a substantially cylindrical magnetic structure functioning as a magnetic shield and a substantially cylindrical electrically conductive structure functioning as an electrostatic shield is disposed on the outside of the magnetic structure. With this unique arrangement, it is possible to sufficiently absorb a radiant noise by the magnetic structure functioning as a magnetic shield. A portion of radiant noise which is not completely absorbed by the substantially cylindrical magnetic structure is completely absorbed by the substantially cylindrical electrically conductive structure, thereby completely inhibiting the radiant noise in the electric cable.
Further, in the radiant noise inhibiting assembly of preferred embodiments of the present invention, only a first end of the electrically conductive structure which is constructed to function as an electrostatic shield is connected to a ground of the electronic device. The first end is closer to the electronic device than a second end of the electrically conductive structure. Thus, the second end of the electrically conductive structure is not grounded. Therefore, it is possible to completely prevent a radiant noise from transmitting through the electrically conductive structure, which provides a function of an electrostatic shield, to an electronic device connected at the front end of the electric cable. Moreover, the radiant noise inhibiting assembly of preferred embodiments of the present invention may be attached to an electric cable within a length of about 1 m from the electronic device, such that the length of the radiant noise inhibiting assembly may be adjusted in accordance with a length of the electric cable and a noise amount required to be inhibited, thereby rendering it possible to sufficiently inhibit a radiant noise in the electric cable.
Further, the radiant noise inhibiting assembly of preferred embodiments of the present invention may be such that the magnetic structure preferably has a substantially annular shape or has a substantially sheet-like shape.
Further, the radiant noise inhibiting assembly of preferred embodiments of the present invention may include a substantially cylindrical case which is constructed such that the electric cable covered by the magnetic structure passes through an internal space of the substantially cylindrical case and the electrically conductive structure is disposed in the substantially cylindrical case, such that the magnetic structure is completely covered by the electrically conductive structure.
Moreover, the radiant noise inhibiting assembly of preferred embodiments of the present invention may be such that the magnetic structure to be received into the substantially cylindrical case is preferably a sheet-like magnetic material having a predetermined flexibility, the magnetic structure is adapted to cover up the outer surface of the electric cable by being wound around the outer surface of the electric cable, or by having a two-layer structure arranged such that the electric cable is sandwiched between the two layers of the two-layer magnetic structure.
Further, the radiant noise inhibiting assembly of preferred embodiments of the present invention may be such that the magnetic structure preferably includes two substantially cylindrical flexible members each having an elongated slot extending from a first end to a second end in a longitudinal direction thereof, a first of the two substantially cylindrical members is positioned on the outside of the electric cable so as to cover the electric cable, a second of the two substantially cylindrical members is positioned on the outside of the first substantially cylindrical member so as to cover main portions thereof including its elongated slot with the electric cable located at the innermost portion thereof.
Moreover, the radiant noise inhibiting assembly of preferred embodiments of the present invention may be such that the magnetic structure may include a plurality of ring-like core members, each of which is a two-piece type ring-like core member including two half-ring core pieces, the substantially cylindrical case is a two-piece type, substantially cylindrical case including two elongated half cylindrical pieces divided in the longitudinal direction thereof. The half-ring core pieces are arranged on the two elongated half cylindrical pieces in a manner such that when the two elongated half cylindrical pieces are closed together to form the cylindrical case, each of the pairs of corresponding half-ring core pieces define one ring-like core member.
Further, the radiant noise inhibiting assembly of preferred embodiments of the present invention may be such that the electric cable is a flat cable, the magnetic structure is a two-layer sheet-like magnetic structure having a predetermined flexibility, and is positioned on both sides of the flat cable in a manner such that the flat cable is sandwiched between two layers of the two-layer sheet-like magnetic structure. The substantially cylindrical case is preferably a flat case including two half case pieces divided in the longitudinal direction thereof. When the two half case pieces are closed together, two longitudinal edge portions of the two-layer sheet-like magnetic structure covering the flat cable are firmly pressed by the two half case pieces of the flat case, thereby forming a closed magnetic circuit around the flat cable.
Moreover, the radiant noise inhibiting assembly of preferred embodiments of the present invention may be such that the flexible magnetic structure is made of a magnetic rubber obtained by mixing and kneading a desired amount of magnetic particles into a rubber.
Further, the radiant noise inhibiting assembly of preferred embodiments of the present invention may be such that the substantially cylindrical case is preferably made of a metal so that the substantially cylindrical case itself can serve as an electrically conductive structure, or the substantially cylindrical case is made of a resin, and a metal film is provided on the surface of such resin case so as to provide an electrical conductivity for the substantially cylindrical case.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.